The science of language, including phonetics, phonology, morphology, syntax, semantics, pragmatics, and historical linguistics. (Random House Unabridged Dictionary, 2d ed)
A verbal or nonverbal means of communicating ideas or feelings.
Collections of facts, assumptions, beliefs, and heuristics that are used in combination with databases to achieve desired results, such as a diagnosis, an interpretation, or a solution to a problem (From McGraw Hill Dictionary of Scientific and Technical Terms, 6th ed).